1. Technical Field
The present invention relates to a television synchronization system and more particularly to a television synchronization system in which a sync signal has bipolar pulses, i.e., positive and negative polarity pulses which are symmetrical, so that a reproduced sync signal synchronously separated from a transmitted television signal has an improved accuracy of phase error.
2. Background Art
So far a television sync signal generally consists of negative polarity pulses only. As a result, the reference phase of a sync signal which is synchronously separated and reproduced from a transmitted television signal varies due to variations in the frequency and amplitude characteristics of a transmission line used to transmit the television signal.
FIGS. 1A and 1B show waveforms of a horizontal sync signal which is used in a conventional television system and is reproduced after transmission.
In FIG. 1A, the normal horizontal sync signal is indicated by the solid line and the intersection 101A of the horizontal sync signal with the reference level indicates the reference phase. The waveform shown by the broken-line is the horizontal sync signal distorted by the transmission line. The intersection 102A of the distorted horizontal sync signal with the reference level indicates a phase which is different from the reference phase.
In FIG. 1B, the horizontal sync signal which is reproduced from the above-described normal horizontal sync signal is indicated by the solid line, while the horizontal sync signal which is reproduced from the distorted horizontal sync signal is indicated by the broken-line. As shown in FIG. 1B, the reproduced phase is shifted due to the distortion and this shift varies depending on changes of the transmission line characteristics
Next, the vertical sync signal will be explained.
FIGS. 2A, 2B and 2C are waveforms showing the vertical sync portion of the composite sync signal used in the conventional television system.
FIG. 2A is the waveform of the vertical sync portion of the composite sync signal in the first field, while FIG. 2B is the waveform of the vertical sync portion of the composite sync signal in the second field.
In order to accomplish the sync separation of the vertical sync signal from the composite sync signal which is transmitted through the transmission line, an integrator, for instance, can be used.
FIG. 2C shows an integrated waveform of a signal obtained by an integration circuit The solid line indicates the integrated waveform of the first field, while the broken-line indicates the integrated waveform of the second field. The vertical sync signal is reproduced in a different phase as indicated by the intersections 201 and 202 with the reference level in FIG. 2C.
In order to prevent such difference in phase, vertical equalizing pulses are added to the composite sync signal, but it has been impossible to completely eliminate the phase difference in the reproduced vertical sync signal in each field.